This invention relates to a method and apparatus for applying cryotherapy and more particularly to apparatus and methods employing specifically shaped elongated tubular needles inserted through the skin of a patient to destroy lesions by passing a cryogen through the needle.
Cryogenics are primarily concerned with the development of freezing temperatures within a biological system. Thus use of cryogenics in medicine dates back to the ancient Egyptians of 2500 BC as they found that the application of cold soothes sites of trauma and reduces inflammation.
See a text entitled "Cryosurgery-For Skin Cancer and Cutaneous Disorders" edited by Setrag A. Zacarian, published by The C. V. Mosby Company (1985), St. Louis, Toronto, Princeton.
The destruction of tissue by local application of refrigerants is an established surgical technique. When controlled, it will provide precise injury and at the same time spare neighboring vital structures.
Cryosurgery is based on withdrawal of heat from a biological system which will lead to freezing of the tissues and transformation of the water from solution into biologically inert ice crystals. In turn this will lead to cessation of circulation in the tissues with intra- and extra-cellular biochemical, anatomical and physiological sequel which will end in tissue anoxemia and ischemic necrosis.
The critical temperature at which cells die when they are frozen may occur between -2.degree. C. and -4.degree. C. It was found that -50.degree. C. is the optimal temperature for achieving effective cryonecrosis of malignant tumors of the skin.
The two most commonly used refrigerants in cryosurgery are nitrous oxide (N.sub.2 O) and liquid nitrogen (LN.sub.2). The latter is the only coolant effective for malignant tumors as it has a lower boiling point up to -195.6.degree. C.
Cryosurgery is used for treating benign, premalignant and some cutaneous malignant lesions. In addition, it was found to be useful for palliative therapy of malignant conditions.
Two main techniques for cryosurgery application are reported in the literature. A spray technique (ST) in which cryogen is applied directly onto the target site and a cryoprobe technique (CP) in which the surface of the previously cooled probe (by the cryogen) is applied to the target site instead of the actual cryogen. See a text entitled "Skin Surgery" edited by E. Epstein, 5th Edition, Charles C. Thomas, publisher, Springfield, Ill.
The shape of the cryolesion (produced by application of either technique to the surface) is hemispherical as the ice front advances from the surface downward. This hemispherical ice ball cannot be perceived during the freezing procedure but it can be balloted by palpitation, which is adequate for the most superficial lesions, but it is of little value for the common nodular carcinomas of the skin which need measuring of the temperature in depth through thermocouple needles or other apparatus. The rate of extension of freezing slows as conditions at the periphery approach equilibrium between heat loss and heat supply by circulation. In general, the depth of freezing may be judged by the lateral spread of frost from the probe and this is used as a guide in treatment. It is just about the radius of the surface area and about half the radius of the ice ball in the cryo-spray technique.
The choice of technique is based in part on technical consideration but also in part on personal preference. The advantage of a probe technique is that it produces a more predictable area freezing, deeper penetration in addition to the possibility of pressure on the probe which increases the depth of penetration through compression of the tissue. Cryo-probes may be either applied to the surface of a lesion or inserted into the tissues (especially pointed probes) to produce deep freezing. Surface freezing with application of slight pressure is used more commonly than probe insertion as it has the advantages that no wound is caused, little or no bleeding occurs, need for anesthesia is lessened and the danger of dissemination of tumor cells are minimized. On the other hand, insertion of the probe into the tissue has its advantage in that it increases efficiency of freezing because of greater contact with the freezing surface.
Presently available probes are employed by application of the probes to the surface of the skin to transmit the cold to deeper tissues. Due to the length of time required, this technique results in damage to the overlying tissue. Such probes are available from many concerns such as the Brymill Corporation of Vernon, Conn. 06066. To achieve cooling of the probe, the gas circulates inside its lumen. The probes contain an inlet conduit and an outlet conduit both of which are associated with a probe tip. Hence, larger probes which can perform deeper penetration are wide and have diameters in excess of 3 mm. Hence, these probes are employed together with surgical procedures using scalpels, punch biopsy, electrocautery and so on. The use of the larger probes is limited due to the attendant surgical procedures requiring a large bleeding field and local anesthesia to enable the probe to be inserted at the proper depth.
There are thin probes which are about 1 mm in diameter and which are cooled by conduction. These probes are extremely short (less than 5 mm) and also require a surgical opening to reach the outer layers of the deeper tissues to be frozen.
The advantage of the spray technique is that the cryogenic agent is used at its coldest possible temperature and the spray can be moved freely about the lesion so that freezing can be extensive and wide rather than deep (as it does not compress tissues). The principal problem with the spray is that freezing is difficult to achieve and prolonged use in one area results in healthy tissue destruction. This is in addition to the possibility of gas insuflation of subcutaneous tissues and the possibility of infection with organisms which the gas may contain (as Staphylococcus albus).
The destruction of a deeper tissue by the commonly used techniques need more destruction of the superficial tissues as the cooling starts from above. This will lead usually to unwanted manifestations and uncommonly to some complications. The undesirable clinical manifestations start by wheal formation due to liberation of histamine from degranulated mast cells. This is usually followed by formation of a bulla due to dermal-epidermal separation while with deeper freezing the blister does not develop. The bulla may be hemorrhagic and sersanguineous exudate may persist coming out up to 10 days or more. Oedema and crust formation usually follow and complete re-epithelization may not take place (in some lesions) before two months of cryosurgery. In addition to the hypertropic scars and pigmentary disorders, other less common complications were reported as: pain, post-operative infection, debilitating oedema, development of pyogenic granuloma, and nerve damage. Also the possibility of nitrogen hypoxia exists when working near the nostrils or mouth. Although success in curing some lesions by cryosurgery (as Actinic Keratosis) may reach up to 98%, the problems of recurrence and incomplete cure differ among the lesions with different pathologic natures.
As a result, many authors did not find the ordinary methods and instrumentations of cryosurgery satisfactory in regard to ease of application, efficacy and optimum cosmetic results. This was especially true of lesions with different groups of patients especially poor risk patients because of the associated diseases and advanced age. So some investigators had been forced to modify the known techniques (ST, CP).
Some of the modifications concerned the instrumentation, as using different probes and using clear plastic cones to allow control of the lateral spray and visualization of the frost during freezing. Other modifications were concerned with the methods of application as debulking of the keratotic lesions, combination of electrocautery or partial excision or curretage with cryotherapy and application of both spray and probe techniques through the biopsy site.
In spite of the available modifications, the problem of producing and determining of effective freezing in depth seems to be still unsolved, a hope which attracted the effort of some investigators.
Some authors tried to use other aids to determine the depth of the ice front. Zacarian D., made an experiment using ultrasound and hoped for a visual demonstration of the evolving cryolesion. But, during the freezing state, the ultrasound was unable to detect the hemispherical ice formation or depth of the ice front below the skin surface and within the tumor. He stated that further devices should include the ability to visualize and measure the volume of the evolving cryolesion and detect the advancing hemispherical ice front during cryosurgery.
Gage A. stated that the chief limitation with cryosurgery is the difficulty in freezing sufficient tissue (especially for large cancers). The best of presently available apparatus is barely adequate because tissues are poor conductors of heat that limits extension of freezing. The amount of tissue that can be frozen in a single application of a probe is small in comparison with many lesions. Depth of freezing beyond 2 cm. is difficult to achieve. Multiple applications of the probe, insertion of the probe into bulky lesions and repetition of freezing at a later date are the methods of compensating for the difficulty of freezing sufficient tissue. Still these do not ensure capability of freezing large cancers. Inevitable advances in equipment design and improved techniques of freezing should help solve these problems.
In the description of the ideal apparatus for the application of liquid nitrogen; Elton R., mentioned that it should be simple to operate, safe to use, portable and should enable the operator to freeze to an adequate depth.
In trained hands cryosurgery has already proved to be a valuable tool. No doubt as improvements in equipment and techniques are developed, it will become even more valuable because of its unique properties.
The problems attendant with commercially available probes have been documented and the need for improved devices has been recognized.
See the following references: